mlx4: Activate SR-IOV mode for IB

Remove the error returns for IB ports from mlx4_ib_add,
mlx4_INIT_PORT_wrapper, and mlx4_CLOSE_PORT_wrapper.

Currently, SRIOV is supported only for devices for which the
link layer is IB on all ports; RoCE support will be added later.

Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: Roland Dreier <roland@purestorage.com>